Apparatus and method of forming an article displaying a self-maintaining and self-monitoring quality feature

ABSTRACT

An article forming apparatus having a self-maintaining and selfmonitoring quality feature and a method of forming an article is disclosed herein. The apparatus includes two reciprocally moving die faces which cooperate with each other in shaping a portion of an article in a predetermined manner. In this regard, one open end portion of an open ended passage or opening provided through one of the two die faces may be utilized in the aforesaid shaping operation. This passage or opening is provided with a flow of gas under pressure, preferably concurrently with the shaping operation of the apparatus, so as to prevent various foreign particles such as, for example, chips or scraps, from lodging or accumulating within or adjacent the passage, which particles might otherwise create an obstruction to the shaping operation, thereby adversely effecting the predetermined shape desired. In addition, the gas pressure within the passage is monitored, preferably continuously, so that, in the event of an obstruction, a signal is produced for terminating operation of the forming apparatus and/or providing an indication to the operator.

United States Patent [1 1 Lind et a1.

[ APPARATUS AND METHOD OF FORMING AN ARTICLE DISPLAYING ASELF-MAINTAINING AND SELF-MONITORING QUALITY FEATURE [75] Inventors:Archie L. Lind, Lakewood; Mack R.

Cobb, Wheatridge, both of C010.

[73] Assignee: Ball-Corporation, Muncie, Ind.

[22] Filed: Dec. 13, 1971 [21] App]. No.: 207,066

[52] U.S. C1 72/4, 72/39, 72/344 [51] Int. Cl. B21c 43/00, B21d 45/00,B2ld 55/00 [58] Field of Search 72/1, 8, 26, 39, 72/45, 344, 345,346;425/136, 137, 153

[56] References Cited UNITED STATES PATENTS 634,412 10/1899 Henderson72/344 2,679,175 5/1954 Davis 72/39 3,541,640 11/1970 Stefaniak et al.425/136 3,552,164 1/1971 Properzi 72/45 3,526,115 9/1970 Armstrong et72/45 3,568,229 3/1971 Moore 10/155 A 3,568,229 3/1971 Moore et al.10/155 A 3,605,473 9/1971 Lyon et a1 72/201 2,347,102 4/1944 Hartmann72/346 3,527,073 9/1970 Wintriss 72/4 3,678,725 7 1972 Langewis 72/344Dec. 25, 1973 Primary ExaminerCharles W. Lanham Assistant ExaminerE. M.Combs me. t.E-..Alb9rs1ins [5 7 ABSTRACT An article forming apparatushaving a self-maintaining and self-monitoring quality feature and amethod of forming an article is disclosed herein. The apparatus includestwo reciprocally moving die faces which cooperate with each other inshaping a portion of an article in a predetermined manner. In thisregard, one open end portion of an open ended passage or openingprovided through one of the two die faces may be utilized in theaforesaid shaping operation. This passage or opening is provided with aflow of gas under pressure, preferably concurrently with the shapingoperation of the apparatus, so as to prevent various foreign particlessuch as, for example, chips or scraps, from lodging or accumulatingwithin or adjacent the passage, which particles might otherwise createan obstruction to the shaping operation, thereby adversely effecting thepredetermined shape desired. 1n addition, the gas pressure within thepassage is monitored, preferably continuously, so that, in the event ofan obstruction, a signal is produced for terminating operation of theforming apparatus and/or providing an indication to the operator.

10 Claims, 2 Drawing Figures PATENTED mes ms 3780.551

1 N VENTORS.

ARCHIE L. LIND MACK R.COBB

Rams M AT TORNEY APPARATUS AND METHOD OF FORMING AN ARTICLE DISPLAYING ASELF-MAINTAINING AND SELF-MONITORING QUALITY FEATURE BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relatesgenerally to an article forming apparatus and more particularly to suchan apparatus having a self-maintaining and self-monitoring qualityfeature.

2. Description of the Prior Art Heretofore, various types of articleforming machines have been developed, some more complicated than others.In any case, many of these machines are utilized for providing, at leastin part, a raised surface such as, for example, what is commonlyreferred to as a button in an otherwise flat portion of an article. Forexample, the ring tab provided with a beverage container lid is, in manycases, secured to the lid by such a button or raised portion.

One typical way in which the aforedescribed raised portion or button isproduced or shaped is by utilizing a press having cooperating male andfemale die components. This, however, has presented, and continuouslypresents, a problem, especially when the opening in the female die issmall in cross section and when the press is operated in an uncleanenvironment such as a typical factory having chips, scraps and othersuch foreign particles which tend to accumulate around the press.Specifically, the chips, scraps and other environmental particles tendto settle around and lodge within the opening provided in the female diewhich, in many instances, prevents the dies from cooperating in themanner intended, thereby degrading the quality of the raised portion orbutton formed, especially where close tolerances are required. Thisproblem can, of course, be costly when considering the large number ofmalformed lids or other articles which could be produced beforediscovery of the'problem. In this regard, there is always danger ofstamping the chips into the article and, in the case of container lids,there is always the possibility that the chips will contaminate thecontained substance.

Another problem presents itself, especially where the article formingoperation is a high speed operation such as in the production ofbeverage container lids. Specifically, the high speed operation makesquality monitoring quite difficult.

SUMMARY OF THE INVENTION The present invention, which providesheretofore unavailable improvements in article forming apparatus,includes a quality self-maintaining and self-monitoring feature whicheliminates many of the foregoing deficiencies of the prior art as wellas other deficiencies thereof.

Accordingly, an object of the present invention is to provide animproved article forming apparatus including a self-maintaining andself-monitoring quality feature.

Another object of the present invention is to provide a new and improvedarticle forming apparatus having a form contributing component which maybe continuously cleansed of foreign particles during the formingoperation of an article so as to minimize the possibility of producing amalformed article otherwise caused by accumulation of the foreignparticles.

Yet another object of the present invention is to provide a new andimproved article forming apparatus having a form contributing componentwhich may be continuously monitored for the presence of foreignparticles during the forming operation of an article so as to minimizethe possibility of producing a malformed article otherwise caused by thepresence of such particles.

Still another object of the present invention is to provide a new andimproved article forming apparatus, the forming operation of which isautomatically terminated in response to the presence of certainparticles which contribute to article malformation.

Yet another object of the present invention is to provide a new andimproved article forming apparatus which is provided with anuncomplicated and economically providable self-monitoring andself-maintaining quality feature.

These and other objects and features of the present invention willbecome apparent from the following descriptions.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an articleforming apparatus constructed in accordance with the present invention;and

FIG. 2 is a sectional view'taken generally along line 2-2 in FIG. I.

DETAILED DESCRIPTION In accordance with the instant invention, anarticle forming apparatus is provided for forming articles ofmanufacture such as, for example, metal beverage container lids havingsnap-off ring tabs from, for example, disc shaped blanks. As will bedescribed hereinafter, the apparatus includes .male and female diecomponents or portions which cooperate with each other and with each ofthe blanks for producing in the latter a raised portion such as, forexample, a button adapted to fasten a ring tab or the like to theultimately formed lid.

Forming apparatus of the type described are often located in factoriesor other environments where matter such as chips, scraps orother foreignparticles is prevalent. It has been found that these foreign particlestend to accumulate around and/or lodge within the form contributingopening defined by the female die component, especially ,where theopening is a blind accumulation thereof and therefore maintainingquality in the forming operation.

However, there may be times when the forming area is so obstructed so asto obstruct the passage and particularly the form contributing endthereof to a sufficient degree so as to prevent suitable formation ofthe aforedescribed button. When this happens, the air pressure in thepassage and in the air line leading to the passage will increase.According to the instant invention, this pressure is monitored,preferably throughout the forming operation, by, for example, a pressuresensitive switch which may be utilized as part of a circuit to warn theoperator of the existing obstruction and/or terminate operation of theforming apparatus so that the obstruction can be eliminated. However, aswill be seen hereinafter, the apparatus of the present invention isdesigned so that the switch will not be affected by momentary closure ofthe opening during forming operations. In this manner, the apparatustakes an uncomplicated and economical approach in maintaining andmonitoring the quality of at least partial article formation. In fact,from the teachings of the instant invention, as set forth in more detailhereinafter, existing article forming apparatus utilizing cooperatingmale and female dies can be economically modified to include theaforedescribed quality maintaining and quality monitoring feature.

Turning now to the drawings, FlG. 1 illustrates an article formingapparatus constructed in accordance with the present invention and isgenerally designated by the reference numeral 10. The apparatus includesa stationary article support or platform 12 which is mounted to anupstanding base 14 and which may be separated around its top surfaceinto a plurality of designated circumferentially spaced formcontributing die portions 16. An index disc 18 displayingcircumferentially spaced pockets 20 extending radially inwardly from itsouter periphery is held contiguous with the top surface of platform 12so as to surround the die portions 16, as illustrated in FIG. 1. Theindex disc is suitably mounted in fixed relationship to the free end ofa shaft 22 so as to rotate therewith and so as to be positioned in theaforestated contiguous manner. The shaft extends downwardly into base 14and, by appropriate conventional means (not shown), is adapted to rotatethe index disc in incremental steps so that the pockets 20 move tosuccessive form contributing die portions.

Article forming apparatus also includes a crosshead assembly 24comprising part of, for example, a conventional minister press. Forpurposes of clarity and brevity only the cross-head assembly of thepress is illustrated. The cross-head assembly, which by conventionalmeans (not shown) is adapted to vertically reciprocate in synchronismwith the incremental rotation of index disc 20, includes a plurality ofcircumferentially spaced cross-heads 26 depending from a support 28 andin vertical alignment with the respective die portions 16. Each of thesecross-heads and corresponding vertically aligned die portions constituteopposing die portions or components in providing a specific formingoperation in the overall formation of an article.

operationally, work pieces such as, for example, disc shaped blanks 30are conveyed from a suitable conveyor mechanism 31 to a receiving area32 comprising a designated segment of the index discs top surface, thereceiving area being surrounded by one of the pockets as illustrated inPK]. 1. The index disc is then rotated by drive shaft 22 in thedirection of arrow 34 so that the blanks are indexed to successive:forming stations which comprise the area between correspondingcross-heads and aligned form contributing die portions. Upon receipt ofthe blanks or partially processed blanks at the various formingstations, rotation of the index disc is terminated for a brief period sothat each of the cross-heads, which is synchronized to reach the bottomof its reciprocating stroke at that time, can engage and, along with theappropriately designed surface making up the die portion, work on arespective blank or partial blank positioned thereunder. The blank orpartially formed blank is thereafter moved in incremental steps to theremaining successive forming stations where it is ultimately formed intoan article 36 such as the aforedescribed metal container lid having, forexample, a snap-off ring tab. After the blanks are formed into articles36, they are moved to a designated exit 38 and thereafter transferred byconventional means (not shown) from the exit area to a second suitableconveyor mechanism 40 which transfers the articles to, for example, apackaging station.

As illustrated in FIG. 2, one of the cross-heads 26 and verticallyaligned form contributing die portions 16 may be utilized for forming araised portion or button in the disc shaped blank 30. Accordingly, thatparticular cross-head may be designed as a male die componentdisplaying, for example, a flat downwardly facing surface 42 with adownwardly projecting portion 44 extending therefrom. 0n the other hand,the corresponding die portion 16, may be designed as a female diecomponent and, in accordance with the present invention, includes anopen ended passage 46 extending from the top form contributing surfaceof the plateform l2 and entirely through the platform. In this regard,the passage, that is, at least the top form contributing end thereof, isdesigned to cooperate with the projecting portion 44 of the cross-headwhen the latter is at the bottom of its reciprocating stroke so as toform the aforestated button.

In accordance with the present invention, a pressurized air supply 48,housed in, for example, a control panel 50, is provided for supplyingair or other suitable gas under constant pressure of, for example, 5 psithrough the passage 46. The air or other gas is directed from the supplyto the bottom open end of the passage by a suitable conduit 52 which isappropriately con nected and sealed at opposite ends to the air supplyand the bottom of platform 12 respectively, as illustrated in FIG. 2,and which is larger in cross-sectional diameter than the passage forpurposes to be described hereinafter. The air supply is opened tothe-passage by, for example, an on-off switch 54 and preferablycontinuously maintained opened during the article forming operation, butmay, for example, by conventional means (not shown), be automaticallyintermittently opened and closed in a predetermined manner. In this way,the air flows upwardly through the passage for cleansing the formingarea, passage and particularly the top form contributing end thereof ofmany foreign particles which might otherwise lodge within the passageand/or around the forming area and cause malformation of the articlesduring forming operation. Accordingly, the quality in which the buttonsare formed may be maintained during operation of the apparatus.

However, there may be an occasion where foreign matter lodges withinpassage 46 and particularly at its form contributing end. If leftunnoticed, this, of course, could cause the production of many malformedarticles Accordingly, apparatus 10 is provided with a pressure switch 56which comprises part of an electrical circuit (not shown) and which maybe of the conventional type such as, for example, one which energizes arelay or relays when actuated by a predetermined pressure. The switch ispositioned, for example, in the line with conduit 52 for monitoring thepressure within the conduit and passage 46. In the event that thepassage is obstructed to a degree sufficient to raise the pressuretherein to a predetermined level such as, for example, from 5 psi topsi, the pressure switch, which is appropriately adjusted, will actuate.In this regard, the air supply 48 would be providing at its output apressure of, for example, to psi so that blockage of passage 46 willallow a pressure build-up therein of at least 10 psi.

The electrical circuit incorporating the switch may include suitableindicating means such as an indicator light 58 which is adapted to lightup or flash if the pressure switch is actuated or a sounding means (notshown) which is adapted to sound an alarm if the switch is actuated. Inaddition thereto or in lieu thereof, the electrical circuitincorporating the pressure switch may be appropriately connectedthrough, for example, conduits 60 and 62 and emergency stop circuits(not shown) to coventional breaking means 61 and 63 for terminatingoperation of the apparatus. When the pressure within the passage andconduit 60 returns to normal operating pressure, the pressure switch canbe manually returned to its initial unactuated operating position or maybe of the type which automatically returns to this position.

In the foregoing manner, apparatus 10 is continuously quality monitoredthroughout its operation. In this regard, it should be noted that thepassage 46 will be periodically blocked by the cross-head 26 when thelatter is in an article engaging position. However, this blockage is ofsuch a short duration that the pressure in the passage will notgenerally build up enough to actuate the switch 56. In addition, asillustrated in FIG. 2, the cross-sectional diameter of conduit 52 islarger than the cross-sectional diameter of passage 46. Hence, thelarger conduit acts as a reservoir so that short durational blockages ofthe passage will not cause an immediate build-up in pressure from, forexample, 5 psi to 10 ps1.

It is to be understood that the present invention is not limited to theparticular typed of article forming apparatus illustrated. Furthermore,it is to be understood that the particular design of passage 46 is notlimited to that shown in FIG. 2 but may be of any suitable design solong as air under pressure may be directed therethrough so as to bothcleanse the passage of various foreign matter as well as monitor thepassage for possible obstructions.

Although a single embodiment of'the present invention has beenillustrated and described, it is anticipated that various changes andmodifications will be apparent to those skilled in the art, and suchchanges may be made without departing from the scope of the invention asdefined by the following claims.

What is claimed is:

1. An article forming apparatus having a selfmaintaining andself-monitoring quality feature, said apparatus comprising: a formingdie arrangement adapted to form at least a portion of an article into apredetermined shape at a forming area, said arrangement including acomponent having an open ended passage extending therethrough; qualityselfmaintaining and self-monitoring means including a pneumatic pressuresource connected to said passage by means of a conduit of across-sectional diameter larger than the cross-sectional diameter ofsaid passage for automatically preventing retention of undesiredparticles in the forming area and pressure responsive means incommunication with said pressure source to indicate pressure increaseswithin said passage above a threshold value resulting from continuingobstruction of said passage due to the retention of said particles inthe forming area.

2. An article forming apparatus according to claim 1 wherein saidforming arrangement includes a second component, at least one of saidfirst-mentioned and second components being adapted for movement betweena first position away from the other component and a second positionadjacent said other component, said second component cooperating withone open end of the gas receiving passage of said first-mentionedcomponent for producing said predetermined design in said article whenthe latter is positioned between said components and when saidcomponents are in said adjacent positions.

3. An article forming apparatus according to claim 2 wherein said secondcomponent includes a projection adapted to enter into a portion of saidpassage through the cooperating open end of said gas receiving passagewhen said components are in said adjacent position whereby to form aprojection in a substantially flat article. I

4. An article forming apparatus having a combination quality maintainingand quality monitoring feature, said apparatus comprising: first andsecond members, at least one of which is adapted-for movement between afirst position away from the other member and a second position adjacentsaid other member, said first member having an open ended passageextending therethrough and at least a portion of said second memberbeing adapted to cooperate with said first member and one open end ofsaid passage when said members are adjacent each other for forming anarticle in a predetermined fashion; means providing a supply of gasthrough said passage for minimizing the accumulation of foreignparticles within said passage whereby to maintain the quality inwhichsaid article is formed; and switch means cooperating with saidlast-mentioned means for providing an indication of a predetermined airpressure buildup in said passage greater than the intermittent airpressure buildup resulting from temporary closure of said passage bysaid second member or said article whereby possible obstruction of thecooperating open end of said passage due to the accumulation of saidparticles therein can be monitored for monitoring the quality in whichmaterial is being formed.

5. An apparatus for forming a projecting portion in a substantially flatarticle, said apparatus comprising:

first and second cooperating forming members, at least one of which isadapted for movement between a first position away from the other memberand a second position adjacent said other member, said first memberhaving an open ended passage extending therethrough and said secondmember having an outwardly projecting portion designed to enter into atleast a portion of said passage from one open end thereof when saidforming members are in said adjacent positions whereby to form aprojecting portion in a substantially flat surface of an article; an.airsupply; conduit of a cross-sectional diameter greater than thecrosssectional diameter of the opening of said passage for providing airunder pressure from said supply to said passage at the other open endthereof whereby to cleanse said passage of various foreign particles andthereby minimize obstruction to the entry into said passage; and meanscooperating with said air supply and said air providing means forproviding an indication in the event that the air pressure within saidpassage reaches a predetermined value greater than that caused byintermittent closure of said passage opening during the formingoperation whereby to monitor a possible obstruction in said passage dueto the retention of said particles therein, said air providing means andair pressure indication means being adapted for continuous operationduring operation of the apparatus whereby to maintain and simultaneouslymonitor the quality in which said projecting portion is formed.

6. An apparatus according to claim wherein said air pressure indicatingmeans includes means for terminating operation of said apparatus in theevent air pressure in said passage reaches said predetermined value.

7. An apparatus according to claim 5 wherein said air pressureindicating means includes a perceptibility device for indicating thepresence of a pressure buildup in said passage equal to saidpredetermined value.

8. A method of forming an article from an article forming apparatushaving a form contributing component including an open ended passageextending therethrough, said method comprising the steps of: positioningan article adjacent the portion of said component defining one open endof said passage; at least momentarily placing said component portion andsaid article into engaging relationship with each other, flowing astream of gas through said passage to automatically cleanse said passageof various foreign particles and monitoring the pressure of said gas insaid passage to determine pressure increases above a predetermined valuegreater than the pressure increase resulting from momentary closure ofsaid passage resulting from said article being positioned intoengagement with said component, to indicate a possible obstruction insaid passage due to the retention of said particles therein.

9. A method of forming an article from an article forming apparatushaving a form contributing component including an open ended passageextending therethrough, said method comprising the steps of: positioningan article adjacent the portion of said component defining one open endof said passage; at least momentarily placing said component portion andsaid article in engaging relationship with each other; passing gas underpressure through said passage to automatically cleanse said passage ofvarious foreign particles; monitoring the pressure within said passage;and actuating a switch means, in the event that the gas pressure withinsaid passage reaches a predetermined value greater than the pressureresulting from momentary closure of said opening during the formingoperation, to provide an indication of a possible obstruction of saidpassage due to the retention of said particles therein.

10. A method according to claim 9 including the step of terminatingoperation of said apparatus in the event that the gas pressure in saidpassage reaches said predetermined value.

1. An article forming apparatus having a self-maintaining andself-monitoring quality feature, said apparatus comprising: a formingdie arrangement adapted to form at least a portion of an article into apredetermined shape at a forming area, said arrangement including acomponent having an open ended passage extending therethrough; qualityself-maintaining and selfmonitoring means including a pneumatic pressuresource connected to said passage by means of a conduit of across-sectional diameter larger than the cross-sectional diameter ofsaid passage for automatically preventing retention of undesiredparticles in the forming area and pressure responsive means incommunication with said pressure source to indicate pressure increaseswithin said passage above a threshold value resulting from continuingobstruction of said passage due to the retention of said particles inthe forming area.
 2. An article forming apparatus according to claim 1wherein said forming arrangement includes a second component, at leastone of said first-mentioned and second components being adapted formovement between a first position away from the other component and asecond position adjacent said other component, said second componentcooperating with one open end of the gas receiving passage of saidfirst-mentioned component for producing said predetermined design insaid article when the latter is positioned between said components andwhen said components are in said adjacent positions.
 3. An articleforming apparatus according to claim 2 wherein said second componentincludes a projection adapted to enter into a portion of said passagethrough the cooperating open end of said gas receivinG passage when saidcomponents are in said adjacent position whereby to form a projection ina substantially flat article.
 4. An article forming apparatus having acombination quality maintaining and quality monitoring feature, saidapparatus comprising: first and second members, at least one of which isadapted for movement between a first position away from the other memberand a second position adjacent said other member, said first memberhaving an open ended passage extending therethrough and at least aportion of said second member being adapted to cooperate with said firstmember and one open end of said passage when said members are adjacenteach other for forming an article in a predetermined fashion; meansproviding a supply of gas through said passage for minimizing theaccumulation of foreign particles within said passage whereby tomaintain the quality in which said article is formed; and switch meanscooperating with said last-mentioned means for providing an indicationof a predetermined air pressure buildup in said passage greater than theintermittent air pressure buildup resulting from temporary closure ofsaid passage by said second member or said article whereby possibleobstruction of the cooperating open end of said passage due to theaccumulation of said particles therein can be monitored for monitoringthe quality in which material is being formed.
 5. An apparatus forforming a projecting portion in a substantially flat article, saidapparatus comprising: first and second cooperating forming members, atleast one of which is adapted for movement between a first position awayfrom the other member and a second position adjacent said other member,said first member having an open ended passage extending therethroughand said second member having an outwardly projecting portion designedto enter into at least a portion of said passage from one open endthereof when said forming members are in said adjacent positions wherebyto form a projecting portion in a substantially flat surface of anarticle; an air supply; conduit of a cross-sectional diameter greaterthan the cross-sectional diameter of the opening of said passage forproviding air under pressure from said supply to said passage at theother open end thereof whereby to cleanse said passage of variousforeign particles and thereby minimize obstruction to the entry intosaid passage; and means cooperating with said air supply and said airproviding means for providing an indication in the event that the airpressure within said passage reaches a predetermined value greater thanthat caused by intermittent closure of said passage opening during theforming operation whereby to monitor a possible obstruction in saidpassage due to the retention of said particles therein, said airproviding means and air pressure indication means being adapted forcontinuous operation during operation of the apparatus whereby tomaintain and simultaneously monitor the quality in which said projectingportion is formed.
 6. An apparatus according to claim 5 wherein said airpressure indicating means includes means for terminating operation ofsaid apparatus in the event air pressure in said passage reaches saidpredetermined value.
 7. An apparatus according to claim 5 wherein saidair pressure indicating means includes a perceptibility device forindicating the presence of a pressure buildup in said passage equal tosaid predetermined value.
 8. A method of forming an article from anarticle forming apparatus having a form contributing component includingan open ended passage extending therethrough, said method comprising thesteps of: positioning an article adjacent the portion of said componentdefining one open end of said passage; at least momentarily placing saidcomponent portion and said article into engaging relationship with eachother, flowing a stream of gas through said passage to automaticallycleanse said passage of various foreign particles and monitoring thepressure of said gas in said paSsage to determine pressure increasesabove a predetermined value greater than the pressure increase resultingfrom momentary closure of said passage resulting from said article beingpositioned into engagement with said component, to indicate a possibleobstruction in said passage due to the retention of said particlestherein.
 9. A method of forming an article from an article formingapparatus having a form contributing component including an open endedpassage extending therethrough, said method comprising the steps of:positioning an article adjacent the portion of said component definingone open end of said passage; at least momentarily placing saidcomponent portion and said article in engaging relationship with eachother; passing gas under pressure through said passage to automaticallycleanse said passage of various foreign particles; monitoring thepressure within said passage; and actuating a switch means, in the eventthat the gas pressure within said passage reaches a predetermined valuegreater than the pressure resulting from momentary closure of saidopening during the forming operation, to provide an indication of apossible obstruction of said passage due to the retention of saidparticles therein.
 10. A method according to claim 9 including the stepof terminating operation of said apparatus in the event that the gaspressure in said passage reaches said predetermined value.